During the past few decades, allergic diseases have increased to almost epidemic proportions and estimates suggest that 20-30% of the total population in many Western countries is affected. The key role played by IgE in initiating the allergic responses is well documented. Upon release from B lymphocytes, IgE binds to the high affinity IgE receptor (FceRI) present on mast cells and basophils. The subsequent cross-linkage of adjacent IgE molecules on these cells by specific allergens then results in their activation, leading to the release of a number of pro-inflammatory mediators (e.g. histamine, leukotrinenes, prostaglandins), as well as key cytokines and chemokines. Consequently, acute local responses are followed by recruitment and activation of other inflammatory cells (e.g. eosinophils, T lymphocytes), thereby amplifying the allergic cascade. Dendritic cells, for example those present at sites of allergic inflammation (e.g. the lung), may also express FceR1 and can use this receptor to selectively and efficiently take up allergens present in immune complexes with IgE and process these allergens selectively for presentation to allergen-specific T-cells, thus providing a mechanism for persistent T-cell activation and pathologic inflammatory responses.
Most current treatment regimens aim at relieving symptoms rather than treating the cause of the disease and are based primarily on the use of antihistamines, antileukotrienes, cromoglycates, beta-agonists and on general anti-inflammatory compounds such as corticosteroids. Although some of the affected patients have their disease under relatively good control with these drugs, their frequency of administration (often daily or even several times a day) often leads to poor patient compliance and subsequent deterioration of the disease. In addition, in some cases such as severe asthma and severe atopic dermatitis, existing therapies are insufficient to control the disease.
Very recently, a monoclonal antibody (omalizumab, also termed E25, marketed under the trade name Xolair®; Presta et al. J Immunol. 1993 Sep. 1; 151(5):2623-32.) gained approval from several agencies around the world, primarily for treatment of severe asthma and rhinitis. Despite showing efficacy against severe asthma, this antibody still has some drawbacks. Firstly, this is a humanized murine monoclonal antibody, and as such, does not entirely preclude immunological reactions in human patients, thus possibly raising some safety concerns. Secondly, the dose of omalizumab used in treating severe asthma is based on both body weight and the level of circulating free IgE. Patients whose body weight and circulating free IgE that deviate from a specified range are recommended not to use this treatment. Those patients that can be treated may require to receive up to three subcutaneous injections once every two weeks. This heavily impacts on the costs of treatment (estimated to range at US$15,000-44,000 annually per patient), as well as on the quality of life of the patients, making it difficult to use as a general strategy for treatment of allergies.
To overcome the problems of high cost and frequent administrations, an alternative is to trigger our own immune system to produce the therapeutic antibodies by vaccination.
In the course of their investigations, previous workers in the allergy field have encountered a number of considerations, and problems, which have to be taken into account when designing new anti-allergy therapies. One of the most dangerous problems revolves around the involvement of IgE cross-linking in the histamine release signal. It is most often the case that the generation of anti-IgE antibodies during active vaccination, are capable of triggering histamine release per se, by the cross-linking of neighbouring IgE-receptor complexes in the absence of allergen. This phenomenon is termed anaphylactogenicity. Indeed many commercially available anti-IgE monoclonal antibodies which are normally used for IgE detection assays, are anaphylactogenic, and consequently useless and potentially dangerous if administered to a patient. Therefore, in order to be safe and effective, the passively administered, or vaccine induced, antibodies must bind in a region of IgE which is capable of inhibiting IgE activities without being anaphylactic per se.
It is therefore desirable to provide a composition, such as an antigenic IgE peptide, or the combination of several thereof, coupled to an immunogenic carrier, and optionally administered with one or more adjuvants, able to induce potent non anaphylactogenic anti-IgE antibodies in an individual capable of significantly reducing levels of circulating free IgE. Increased potency would typically result in the following benefits: lower doses required to achieve clinical benefits, lower volume of injection required e.g. for subcutaneous or intramuscular administration (compared to monoclonal antibody therapies, for example), lower cost of treatment, increased chances of treatment success, decreased frequency of administration in the treatment regimen, thus providing access to treatment to a wider population of patients, including patients with higher body weight and/or high levels of circulating IgE, and improving patients' quality of life.